Lots of 1804 and 1806 motors in the market shipped with 4mm prop shaft because most of them just copied the design from a famous brand but in fact how many of you use a propeller with 4mm hole? So it does not really make sense to a 5mm adapter ring on a 4mm shaft.

So here you are. This 5mm Propeller Mount is a spare part of RCX H1806 motor but it is also suitable for many other motors in the market. The base and the bullet designed with pattern for "Anti Slip" which means it locks up the prop even better than the one you are now using.

You can use this prop mount as long as your motor meets the followings